Structure from Shadow Motion

In outdoor images, cast shadows define 3D constraints between the sun, the points casting a shadow, and the sur-faces onto which shadows are cast. This cast shadow struc-ture provides a powerful cue for 3D reconstruction, but re-quires that shadows be tracked over time, and this is dif-ficult as shadows have minimal texture. Thus, we develop a shadow tracking system that enforces geometric consis-tency for each track and then combines thousands of track-ing results to create a 3D model of scene geometry. We demonstrate reconstruction results on a variety of outdoor scenes, including some that show the 3D structure of oc-cluders never directly observed by the camera. 1